Jacksonville
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Jacksonville clear sky chart from 2005-11-06 to 2025-09-04.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.

Observation Type	Minimum conditions for hour to be usable				Out of hours
	Clear of Clouds	Transparency	Seeing	Sky Brightness
Planetary:	50%	(no limit)	Average	(no limit)	Nighttime Hours
Deep Sky:	70%	Average	(no limit)	5.9	Nighttime Hours
CCD Imaging:	70%	Below Average	Poor	(no limit)	Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

By Month

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

		Occurrence of each Forecast	Data Points
Cloud Cover	Day	9% 6% 2 7% 5% 5% 6% 5% 7% 9% 40%	125911
	Night	10% 6% 2 6% 5% 5% 5% 4 6% 9% 43%	122815
Transparency	Day	38% 9% 15% 18% 14% 6%	129622
	Night	36% 8% 15% 18% 15% 7%	127173
Seeing	Day	10% 7% 22% 26% 22% 13%	16569
	Night	11% 6% 21% 32% 25% 5%	26603

By Month

Percentage Cloud Cover SE (2006-)
Color Meanings: Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	9% 6% 2 4 2 3 3 2 4 5% 58%	4056
	11th to 20th	Day	19% 8% 3 7% 4 4 3 2 4 6% 39%	4060
	21st to end	Day	11% 6% 3 6% 3 3 4 3 5% 8% 48%	4466
February	1st to 10th	Day	14% 7% 2 6% 4 4 3 4 5% 6% 44%	1995
	11th to 20th	Day	12% 6% 2 5% 3 4 3 3 5% 6% 49%	1948
	21st to end	Day	12% 6% 2 6% 3 4 4 3 5% 5% 48%	1726
March	1st to 10th	Day	14% 8% 3 7% 4 4 4 3 5% 7% 40%	4935
	11th to 20th	Day	7% 3 2 4 3 3 4 4 5% 8% 58%	4980
	21st to end	Day	12% 6% 2 5% 4 4 4 3 5% 9% 46%	5465
April	1st to 10th	Day	8% 6% 2 5% 5% 4 4 4 6% 8% 48%	2200
	11th to 20th	Day	8% 6% 3 7% 4 5% 5% 4 6% 8% 45%	2244
	21st to end	Day	5% 4 1 5% 4 5% 5% 5% 7% 10% 51%	2439
May	1st to 10th	Day	7% 5% 2 6% 5% 5% 5% 5% 7% 10% 44%	5862
	11th to 20th	Day	10% 5% 2 6% 4 4 5% 4 6% 10% 43%	5861
	21st to end	Day	4 3 2 6% 5% 6% 6% 5% 8% 12% 43%	6433
June	1st to 10th	Day	11% 6% 2 7% 8% 7% 6% 7% 8% 9% 29%	2600
	11th to 20th	Day	5% 4 2 7% 7% 8% 8% 7% 9% 12% 31%	2600
	21st to end	Day	6% 6% 3 9% 7% 7% 8% 6% 9% 11% 28%	2600
July	1st to 10th	Day	7% 7% 3 10% 7% 8% 9% 7% 11% 12% 18%	5900
	11th to 20th	Day	3 3 2 7% 7% 7% 8% 7% 10% 14% 31%	5900
	21st to end	Day	3 4 2 7% 7% 7% 8% 6% 9% 14% 33%	6424
August	1st to 10th	Day	11% 6% 3 8% 7% 7% 7% 6% 9% 12% 23%	4234
	11th to 20th	Day	6% 4 2 7% 6% 6% 7% 6% 8% 12% 36%	4151
	21st to end	Day	8% 5% 2 9% 7% 7% 8% 7% 9% 11% 27%	3961
September	1st to 10th	Day	11% 8% 3 9% 7% 8% 8% 6% 8% 10% 23%	2123
	11th to 20th	Day	14% 8% 3 9% 7% 7% 7% 6% 8% 9% 23%	2090
	21st to end	Day	12% 7% 3 9% 6% 6% 5% 5% 6% 7% 34%	2090
October	1st to 10th	Day	13% 6% 3 7% 6% 6% 6% 4 7% 8% 35%	2052
	11th to 20th	Day	7% 5% 2 5% 4 5% 5% 3 5% 8% 50%	1900
	21st to end	Day	9% 6% 2 6% 4 3 5% 4 5% 8% 49%	2090
November	1st to 10th	Day	11% 5% 2 6% 5% 4 5% 4 5% 8% 45%	1957
	11th to 20th	Day	11% 6% 2 7% 5% 6% 4 4 5% 8% 42%	2000
	21st to end	Day	11% 7% 3 7% 4 4 4 4 6% 6% 45%	1800
December	1st to 10th	Day	6% 4 1 5% 4 4 4 4 6% 8% 55%	2930
	11th to 20th	Day	14% 8% 2 8% 5% 4 5% 4 5% 7% 38%	3373
	21st to end	Day	14% 9% 3 7% 4 4 4 3 5% 6% 41%	4466
January	1st to 10th	Night	9% 6% 2 4 3 3 2 2 4 6% 58%	5889
	11th to 20th	Night	16% 8% 2 7% 5% 4 5% 4 6% 7% 34%	5900
	21st to end	Night	14% 7% 2 6% 4 3 4 4 5% 8% 44%	6490
February	1st to 10th	Night	13% 7% 2 6% 5% 4 3 3 5% 6% 46%	2400
	11th to 20th	Night	13% 7% 3 6% 4 4 3 3 4 6% 47%	2338
	21st to end	Night	11% 7% 2 6% 5% 3 5% 2 5% 6% 48%	1901
March	1st to 10th	Night	18% 9% 3 6% 4 4 3 3 4 5% 41%	4918
	11th to 20th	Night	6% 5% 1 5% 3 3 4 4 6% 9% 55%	4980
	21st to end	Night	9% 6% 2 5% 4 4 4 4 5% 6% 50%	5467
April	1st to 10th	Night	8% 5% 1 5% 5% 4 5% 4 6% 8% 49%	2200
	11th to 20th	Night	9% 5% 2 6% 4 3 4 3 4 7% 53%	2102
	21st to end	Night	6% 3 1 4 3 4 4 5% 8% 8% 53%	1975
May	1st to 10th	Night	5% 4 2 6% 5% 4 4 4 6% 11% 47%	4033
	11th to 20th	Night	10% 6% 2 6% 4 4 4 4 7% 10% 43%	4032
	21st to end	Night	4 4 2 5% 4 5% 4 4 7% 12% 50%	4421
June	1st to 10th	Night	10% 5% 2 6% 5% 4 6% 6% 8% 12% 37%	1800
	11th to 20th	Night	5% 6% 2 6% 5% 7% 7% 6% 9% 13% 35%	1800
	21st to end	Night	7% 5% 2 6% 6% 6% 5% 5% 10% 12% 35%	1800
July	1st to 10th	Night	8% 7% 3 9% 8% 7% 8% 7% 10% 10% 24%	4058
	11th to 20th	Night	3 4 2 7% 6% 6% 7% 6% 11% 14% 34%	4057
	21st to end	Night	5% 5% 2 8% 6% 6% 7% 6% 10% 12% 34%	4427
August	1st to 10th	Night	9% 7% 3 9% 6% 6% 6% 6% 9% 12% 26%	2915
	11th to 20th	Night	4 5% 2 6% 4 5% 7% 6% 8% 12% 41%	2875
	21st to end	Night	7% 6% 2 6% 6% 6% 6% 5% 8% 11% 37%	3920
September	1st to 10th	Night	11% 7% 3 8% 6% 6% 7% 6% 7% 11% 28%	2124
	11th to 20th	Night	11% 8% 3 9% 7% 7% 6% 6% 7% 10% 27%	2090
	21st to end	Night	9% 6% 3 7% 5% 6% 6% 4 7% 8% 40%	2090
October	1st to 10th	Night	12% 6% 3 8% 4 5% 5% 4 6% 6% 41%	2127
	11th to 20th	Night	7% 5% 2 6% 4 4 4 3 5% 7% 54%	2280
	21st to end	Night	8% 5% 2 6% 4 3 4 3 5% 8% 51%	2508
November	1st to 10th	Night	11% 5% 2 6% 5% 4 4 4 5% 8% 47%	2341
	11th to 20th	Night	11% 6% 3 7% 3 4 4 4 5% 6% 46%	2400
	21st to end	Night	12% 6% 2 5% 4 5% 4 3 5% 8% 46%	2595
December	1st to 10th	Night	10% 5% 2 5% 4 4 3 3 4 6% 54%	4250
	11th to 20th	Night	13% 9% 3 7% 4 4 3 3 5% 6% 45%	4822
	21st to end	Night	13% 9% 3 7% 4 4 4 3 5% 6% 40%	6490

Transparency (when cloud cover <= 30%)
Color Meanings: Too cloudy to forecast Poor Below Average Average Above average Transparent
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	29% 3 8% 16% 28% 16%	4057
	11th to 20th	Day	47% 4 4 13% 20% 12%	4060
	21st to end	Day	35% 5% 8% 23% 17% 11%	4466
February	1st to 10th	Day	41% 6% 9% 14% 21% 10%	1995
	11th to 20th	Day	36% 5% 9% 16% 23% 12%	1958
	21st to end	Day	36% 5% 11% 17% 19% 13%	1726
March	1st to 10th	Day	43% 5% 11% 14% 18% 9%	4935
	11th to 20th	Day	24% 4 13% 19% 20% 20%	4980
	21st to end	Day	35% 5% 10% 21% 18% 11%	5465
April	1st to 10th	Day	32% 6% 11% 20% 19% 11%	2200
	11th to 20th	Day	36% 6% 9% 19% 21% 9%	2244
	21st to end	Day	27% 6% 13% 23% 23% 8%	2439
May	1st to 10th	Day	32% 9% 17% 25% 13% 3	5897
	11th to 20th	Day	35% 7% 15% 29% 13% 1	5865
	21st to end	Day	28% 10% 17% 28% 15% 2	6447
June	1st to 10th	Day	46% 12% 17% 16% 9% 1	2600
	11th to 20th	Day	37% 16% 21% 21% 5%	2600
	21st to end	Day	43% 15% 22% 13% 6%	2600
July	1st to 10th	Day	49% 18% 24% 9% 1	5835
	11th to 20th	Day	36% 16% 35% 11% 2	5831
	21st to end	Day	35% 16% 28% 19% 3	6240
August	1st to 10th	Day	48% 13% 27% 11% 1	4221
	11th to 20th	Day	36% 13% 23% 19% 9%	4190
	21st to end	Day	44% 14% 18% 21% 2	3961
September	1st to 10th	Day	52% 14% 16% 10% 7% 1	2123
	11th to 20th	Day	53% 14% 14% 13% 6%	2090
	21st to end	Day	46% 8% 14% 16% 13% 2	2090
October	1st to 10th	Day	51% 8% 9% 10% 15% 7%	3416
	11th to 20th	Day	28% 5% 7% 16% 32% 12%	3140
	21st to end	Day	25% 4 7% 21% 34% 8%	3428
November	1st to 10th	Day	36% 6% 11% 19% 18% 10%	1957
	11th to 20th	Day	40% 6% 9% 15% 20% 11%	2000
	21st to end	Day	39% 5% 10% 18% 21% 8%	1800
December	1st to 10th	Day	28% 5% 13% 24% 20% 10%	2930
	11th to 20th	Day	43% 7% 10% 15% 17% 8%	3370
	21st to end	Day	45% 4 8% 19% 19% 6%	4466
January	1st to 10th	Night	29% 3 8% 12% 35% 13%	5889
	11th to 20th	Night	48% 4 7% 15% 19% 7%	5900
	21st to end	Night	39% 6% 9% 19% 16% 11%	6490
February	1st to 10th	Night	39% 6% 9% 16% 20% 11%	2400
	11th to 20th	Night	38% 6% 8% 18% 18% 12%	2339
	21st to end	Night	36% 5% 10% 20% 18% 11%	1901
March	1st to 10th	Night	45% 4 9% 16% 15% 11%	4918
	11th to 20th	Night	25% 5% 13% 20% 19% 18%	4980
	21st to end	Night	34% 5% 11% 18% 18% 13%	5467
April	1st to 10th	Night	31% 7% 14% 21% 17% 11%	2200
	11th to 20th	Night	31% 6% 10% 23% 21% 10%	2102
	21st to end	Night	25% 8% 15% 27% 20% 5%	1975
May	1st to 10th	Night	29% 11% 20% 26% 12% 3	4060
	11th to 20th	Night	34% 8% 19% 27% 11% 1	4033
	21st to end	Night	26% 8% 20% 28% 18% 1	4429
June	1st to 10th	Night	36% 12% 24% 19% 9%	1800
	11th to 20th	Night	37% 13% 23% 22% 5%	1800
	21st to end	Night	36% 15% 25% 18% 5% 1	1800
July	1st to 10th	Night	48% 17% 24% 9% 1	4015
	11th to 20th	Night	34% 18% 34% 12% 2	4006
	21st to end	Night	37% 14% 26% 21% 2	4297
August	1st to 10th	Night	45% 14% 30% 9% 2	2904
	11th to 20th	Night	32% 14% 25% 20% 9%	2902
	21st to end	Night	38% 13% 25% 21% 3	3920
September	1st to 10th	Night	46% 15% 20% 13% 5% 1	2124
	11th to 20th	Night	48% 14% 17% 14% 6%	2090
	21st to end	Night	38% 11% 14% 21% 14% 3	2090
October	1st to 10th	Night	50% 9% 10% 12% 13% 7%	3543
	11th to 20th	Night	28% 5% 6% 17% 35% 9%	3779
	21st to end	Night	23% 5% 8% 21% 33% 10%	4120
November	1st to 10th	Night	34% 7% 10% 20% 17% 11%	2341
	11th to 20th	Night	38% 6% 8% 17% 21% 10%	2400
	21st to end	Night	37% 5% 12% 19% 18% 9%	2595
December	1st to 10th	Night	31% 4 11% 21% 18% 14%	4250
	11th to 20th	Night	41% 5% 10% 21% 15% 9%	4824
	21st to end	Night	44% 5% 11% 18% 17% 5%	6490

Seeing (when cloud cover <= 80%)
Color Meanings: Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	12% 14% 48% 21% 4 1	300
	11th to 20th	Day	9% 13% 42% 25% 10% 2	300
	21st to end	Day	15% 18% 46% 17% 3	330
February	1st to 10th	Day	12% 15% 36% 27% 8% 1	300
	11th to 20th	Day	16% 14% 41% 21% 8%	300
	21st to end	Day	11% 14% 36% 30% 9% 1	325
March	1st to 10th	Day	13% 15% 33% 28% 11% 1	500
	11th to 20th	Day	14% 11% 33% 27% 13% 3	500
	21st to end	Day	12% 14% 33% 25% 16% 1	550
April	1st to 10th	Day	11% 12% 33% 26% 15% 2	500
	11th to 20th	Day	8% 12% 31% 27% 15% 7%	492
	21st to end	Day	5% 7% 27% 32% 18% 11%	500
May	1st to 10th	Day	4 8% 26% 33% 20% 9%	503
	11th to 20th	Day	9% 3 22% 31% 24% 11%	527
	21st to end	Day	7% 4 13% 27% 31% 17%	573
June	1st to 10th	Day	12% 4 12% 30% 25% 17%	530
	11th to 20th	Day	5% 2 15% 23% 29% 25%	530
	21st to end	Day	5% 2 10% 23% 34% 26%	530
July	1st to 10th	Day	5% 2 7% 18% 34% 34%	525
	11th to 20th	Day	4 1 4 17% 37% 36%	524
	21st to end	Day	5% 2 5% 20% 38% 29%	576
August	1st to 10th	Day	11% 1 8% 21% 32% 28%	526
	11th to 20th	Day	6% 2 4 19% 33% 36%	519
	21st to end	Day	10% 2 8% 23% 30% 27%	583
September	1st to 10th	Day	13% 4 9% 19% 27% 27%	502
	11th to 20th	Day	14% 4 12% 26% 27% 17%	490
	21st to end	Day	14% 3 10% 25% 32% 16%	490
October	1st to 10th	Day	16% 6% 23% 29% 21% 6%	490
	11th to 20th	Day	7% 8% 21% 31% 27% 6%	490
	21st to end	Day	10% 5% 24% 35% 21% 5%	539
November	1st to 10th	Day	16% 7% 24% 30% 19% 5%	495
	11th to 20th	Day	14% 10% 29% 29% 14% 3	500
	21st to end	Day	10% 13% 35% 29% 11% 1	300
December	1st to 10th	Day	9% 14% 33% 26% 15% 2	300
	11th to 20th	Day	17% 13% 34% 30% 5% 1	300
	21st to end	Day	16% 12% 31% 29% 10% 2	330
January	1st to 10th	Night	14% 12% 34% 30% 9% 1	800
	11th to 20th	Night	13% 12% 28% 36% 11% 1	800
	21st to end	Night	16% 11% 36% 30% 6%	880
February	1st to 10th	Night	16% 8% 30% 36% 11%	800
	11th to 20th	Night	16% 11% 33% 34% 7%	783
	21st to end	Night	14% 10% 36% 35% 6%	660
March	1st to 10th	Night	11% 10% 32% 38% 9%	800
	11th to 20th	Night	10% 11% 34% 34% 11% 1	800
	21st to end	Night	11% 8% 32% 37% 12% 1	880
April	1st to 10th	Night	9% 9% 33% 38% 11% 1	800
	11th to 20th	Night	10% 9% 29% 35% 17% 1	791
	21st to end	Night	6% 5% 27% 44% 18% 1	775
May	1st to 10th	Night	5% 3 21% 46% 24% 2	600
	11th to 20th	Night	7% 3 18% 38% 30% 4	591
	21st to end	Night	7% 1 10% 35% 40% 7%	650
June	1st to 10th	Night	12% 2 10% 35% 36% 6%	600
	11th to 20th	Night	7% 2 9% 28% 41% 14%	600
	21st to end	Night	7% 2 8% 26% 43% 14%	600
July	1st to 10th	Night	6% 2 6% 24% 44% 17%	585
	11th to 20th	Night	5% 1 3 18% 52% 21%	582
	21st to end	Night	5% 1 4 21% 55% 13%	657
August	1st to 10th	Night	7% 1 5% 21% 50% 16%	597
	11th to 20th	Night	5% 1 4 20% 50% 21%	594
	21st to end	Night	12% 1 9% 22% 40% 16%	869
September	1st to 10th	Night	12% 2 8% 23% 42% 13%	773
	11th to 20th	Night	13% 3 8% 29% 36% 10%	760
	21st to end	Night	12% 2 11% 29% 37% 9%	760
October	1st to 10th	Night	14% 3 17% 33% 30% 3	760
	11th to 20th	Night	9% 5% 16% 37% 29% 4	760
	21st to end	Night	9% 4 20% 37% 27% 2	836
November	1st to 10th	Night	13% 5% 24% 33% 23% 2	780
	11th to 20th	Night	13% 8% 25% 33% 20% 1	800
	21st to end	Night	12% 8% 28% 33% 18% 1	800
December	1st to 10th	Night	14% 8% 27% 31% 19% 2	800
	11th to 20th	Night	14% 9% 25% 34% 16% 2	800
	21st to end	Night	15% 10% 26% 35% 13%	880

Page generated at 2025-09-01 01:51:08. Version ac07

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